As generally used, such timers have a block-like structure with smooth sides and, for pneumatic control systems, are placed right next to each other or next to other control parts so that only the front ends or face plates of the timer may be seen and may be freely accessed, with the adjustment knobs for the chokes on them.
Such timers are produced with a wide range of adjustment of the time and in view of the great effects which even small tolerances in making the timers have on the times selected on the timers, it is frequently necessary for a stop-watch to be used for checking out the preset time, and not simply to make use of the scale on the timer. Checking out a slow timer (whose preset time may go up to some minutes) is a slow process, because in the case of known timers, it is only when the preset time has run to an end that it is possible to see if the adjustment of the timer is right. The fact that the preset time has run to an end will be seen because of a load being turned on or because of the next stage in a pneumatic program control system being put into operation. It is more specially on checking out the operation of a pneumatic program control system having a number of such timers non-linearly cascaded together that such adjustment is likely to be a very slow process.